Intraocular pressure recording system

ABSTRACT

A new noninvasive approach for intraocular pressure (IOP) measurement allowing continuous monitoring over prolonged periods, regardless of patient&#39;s position and activities. The key element of this measurement method is a soft contact lens ( 1 ) including at least one strain gage ( 2 ) longitudinally arranged around the center of the contact lens and capable of measuring precisely spherical deformations of the eyeball induced by the changes in IOP. This information is transmitted with wires or (preferably) wirelessly in real time to an external recording system ( 14 ). The system is placed in the same way as a normal corrective contact lens, no anesthesia is required and patient vision remains almost completely unimpaired.

FIELD OF THE INVENTION

[0001] The present invention relates to a device for recording theintraocular pressure over a period of time. More precisely, theinvention relates to a device which can be placed on a contact lens onan eye to continuously monitor and record intraocular pressure over anextended period of time, e.g. 24 hours or more.

STATE OF THE ART

[0002] Glaucoma is a widespread disease (2-4% of a given population)characterized by an elevated intraocular pressure (IOP). This elevatedIOP produces a gradual loss of peripheral vision.

[0003] There is therefore a need to have a detailed knowledge of IOP inglaucoma patients in order to provide reliable diagnostics or forsetting up new therapies.

[0004] U.S. Pat. No. 5,179,953 discloses an intraocular pressurerecording system made of scleral contact lens comprising a pressuretransducer including one semiconductor strain gage which indents thesclera in a fixed position. This results in a fixed indentationconnection of the gage to the sclera.

[0005] U.S. Pat. No. 4,089,329 discloses an intraocular pressurerecording system made of a support, e.g. a ring, comprising aplanar-faced pressure transducer which is adapted to crush (flatten) aportion of the scleral surface.

[0006] U.S. Pat. No. 4,922,913 discloses an intraocular pressurerecording system made of a semi-rigid contact lens which contains apressure transducer, e.g. a piezo-electric strain gage, which has aplanar surface flattening a central portion of the cornea.

[0007] The publication entitled “Intraocular pressure measurement withinstrumented contact lenses, Investigative Ophthalmology”, April 1974,pp. 299-302, Vol. 13, No 4. discloses an intraocular pressure recordingsystem made of a contact lens on which a strain gage is placed in ameridional angle of the corneosciera junction to measure angularchanges. This pressure measurement relies on the theoretically predictedcorrelation between IOP and angular changes.

[0008] The publication entitled “A scleral buckle pressure gauge forcontinuous monitoring of intraocular pressure”, Myron et al.,International Ophthalmology 2, 3: 11-17 (1980), discloses an implantablevariable resistance pressure gage made of a strip which is has to beplaced and attached around the periphery of the sclera by a surgeon.

[0009] The publication entitled “Distensibility measurements of therabbit eye”, Tittel & Richards, Investigative Ophthalmology, 1971, vol.10, No 10, 800-809, discloses the use of a circumference gage of thesame type of the scleral buckle pressure gauge which was implanted onrabbits.

[0010] The currently used devices are either too aggressive for thepatient or not accurate enough or do necessitate to topicallyanesthetize the patient's eye and/or to surgically operate prior totesting.

[0011] Thus there is presently a need for a comfortable and accuratetesting which simultaneously does not require a physician.

[0012] The present invention is directed to meeting the above citedneeds. It concerns an intraocular pressure recording system comprising asoft contact lens and an active strain gage fixed to said contact lens,characterized by the fact that said active strain gage has a circulararc shape and is situated around the center of said soft contact lens.This particular configuration allows to measure very precisely sphericaldeformations of the eyeball which are correlated to IOP.

[0013] Using the object of the present invention allows a more accuratemeasurement of the eyeball and i.e. the IOP. Furthermore, due to thefact that the strain gage is not in direct contact with the eye, thepatient feels very comfortable and his vision remains almost completelyunimpaired. In fact he has a similar feeling as a person wearing usualcontact lenses.

[0014] In a preferred embodiment, the active strain gage is made of aresistive metal, the gage resistance varying according to the gagestrain.

[0015] Preferably the active strain gage is a continuous longitudinalelement, e.g. a wire or a microfabricated object (MEMS) which result ina foil strain gage on which a metallic layer is deposited or laminatedon a substrate (e.g. polyimide) and patterned by wet or dry etch in adesired configuration (grid).

[0016] The wire diameter may be comprised between 0.01 mm and 0.1 mm.

[0017] MEMS gages are manufactured according to Integrated Circuitmanufacturing processes, this technique offers the following advantages:Every single parameter of the strain gage can be controlled veryprecisely (e.g. thickness of the metallic strain gage layer) as well thedesign of the grid that can be realized with a precision of about 1 μmand gives the possibility to built really specific gages. Moreover theprocess is completely and easily reproducible.

[0018] As material which can be used for the gages of the presentinvention we can cite Polyimide as substrate and platinum as metalliclayer, but any kind of resistive material as well as semiconductor orresistive polymer could be used. Polyimide as substrate is reallysuitable because it is well known and used in MEMS technology and it isbiocompatible as well as platinum which has also a good strain gagefactor.

[0019] For a variable resistance pressure gage, in order to have a moreaccurate measurement, the gage resistance has to be maximized and itsgrid area has to cover all the zones which have to be monitored. In thepresent invention, this can be achieved by folding the longitudinalelement into several portions which are arranged parallel to each other.

[0020] In one preferred embodiment the active gage forms almost acomplete circle.

[0021] Several active gages can be placed on the contact lens. They canconsist of several circular arc portion placed along the samecircumference or they consist of several concentric circles.

[0022] In another embodiment, the intraocular pressure recording systemfurthermore comprises passive strain gages for thermal compensationwhich has preferably a general circular arc shape made of a continuousmeridional element placed in such a way that several of its portions areradially arranged, i.e. their direction cross the lens center C. Such aconfiguration results in a more accurate measurement.

[0023] In another preferred embodiment, the intraocular pressurerecording system comprise four gages in a Wheatstone Bridgeconfiguration, e.g. two active gages and two passives ones being placedalternatively on the bridge.

[0024] The active gage(s) can be placed at any distance from the centerof the contact lens. In a preferred embodiment, the active gage isshaped in order to be placed on the corneoscleral junction whichrepresents a zone where changes in IOP induce maximum cornealdeformation.

[0025] The gage(s) can be fixed to the lens by any method. It/They canbe first fixed to a substrate which is then fixed on the lens or it/theycan be directly fixed to the lens.

[0026] The data transmission with the gage(s) can be achieved in using awire transmission or (preferably) a wireless transmission system.

[0027] In addition to the gage(s) the contact lens can also compriseother measuring devices such as an ElectroRetinoGraph or a chemicalanalysis sensor.

[0028] The present invention will be more fully appreciated from thefollowing detailed examples taken together with the drawings in which

[0029]FIG. 1 shows a first intraocular pressure recording systemaccording to the invention.

[0030]FIG. 2 shows a second intraocular pressure recording systemaccording to the invention.

[0031]FIG. 3 shows a third intraocular pressure recording systemaccording to the invention.

[0032]FIG. 4 shows a strain gage which can be used with the presentinvention.

[0033]FIG. 5 shows another strain gage which can be used with thepresent invention.

[0034]FIG. 6 shows a simplified block diagram of an intraocular pressurerecording system according to the invention with a telemetry systemembedded and extracorporal receiving units.

[0035] As shown in FIG. 1 to 3, the intraocular pressure recordingsystem comprises a soft contact lens 1 including a circular activestrain gage 2 disposed around the lens center C. Active strain gage 2 ismade of a continuous longitudinal wire which is folded in such a waythat several of its portions 3 are parallel to each other and thereforeconcentric. Both ends 4 of the wire are connected to a data transmissionsystem (not illustrated). The transmission may be achieved via awireless telemetry system.

[0036]FIGS. 2 and 3 illustrate another preferred device similar to theone of FIG. 1 but comprising four gages in a Wheatstone Bridgeconfiguration, e.g. two active gages and two passives ones being placedalternatively on the bridge The passive strain gages 5 are made of acontinuous wire folded into several portions 7 which are radiallyarranged, i.e. their direction cross the lens center C. The wireportions of active and passive gages can be very close to minimize thegage area or more spaced to maximize thermal exchanges and gage area.FIG. 3 shows a configuration with a quite big passive gage area withwire portions grouped into more blocks 6. With such configurations(FIGS. 2 and 3), the two active strain gages 2 measures one type ofstrain (the strongest one) and double the sensivity of the measure onthe Wheatstone Bridge. The two passive strain gages 5 measures anothertype of strain (the weakest one) and compensate for thermal derivation,active and passive gages having the same resistance value without anystress applied.

[0037]FIG. 4 illustrates a strain gage 8 which is made of a wire 10 andFIG. 5 illustrates another strain gage 9 (MEMS) with its grid 11 whichis made according to a micromachining process.

[0038]FIG. 6 shows the simplified block diagram of a preferredconfiguration of the entire system with a telemetry system embedded andextracorporal receiving units. The contact lens comprise the sensor, itis to say active 2 and passive 5 gages on a Wheatstone Bridgeconfiguration, a low-power transponder 12 and a loop antenna 13.Powering and communication are performed contaclessly between thetransponder and an extracorporal mobile interrogation unit (MIU) 14 viacoupled loop antennas. The MIU provides the sensor with energy andpasses the received transponder data to the stationary data receiver(SDR) 15 via a second RF link. The SDR completes the monitoring setup.It stores and displays the received data.

1. Intraocular pressure recording system comprising a soft contact lens(1) such as a silicone contact lens and an active strain gage (2) fixedto said contact lens (1), characterized by the fact that said activestrain gage (2) has a circular arc shape and is situated around thecenter (C) of said soft contact lens (1).
 2. Intraocular pressurerecording system according to claim 1 wherein said active strain gage(2) is made of a resistive material, such as a metal or an alloy. 3.Intraocular pressure recording system according to claim 2 wherein saidactive strain gage (2) is a continuous longitudinal element. 4.Intraocular pressure recording system according to claim 3 wherein saidcontinuous longitudinal element is placed in such a way that several ofits portions (3) are disposed parallel to each other.
 5. Intraocularpressure recording system according to any of the previous claims 1 to 4wherein said active strain gage (2) has a circular shape.
 6. Intraocularpressure recording system according to any of the previous claims 1 to 5further comprising a passive strain gage (5).
 7. Intraocular pressurerecording system according to claim 6 wherein said passive strain gage(5) has a general circular arc shape made of a continuous meridionalelement placed in such a way that several of its portions (7) areradially arranged.
 8. Intraocular pressure recording system according toany of the previous claims 1 to 7 wherein said active strain gage (2) isshaped in order to be placed on the corneosclera junction. 9.Intraocular pressure recording system according to any of the previousclaims 1 to 8 including a wireless telemetry system (12-15) for datatransmission with said strain gage(s) (2,5).
 10. Intraocular pressurerecording system according to any of the previous claims 1 to 9 whereinat least one of said continuous longitudinal or meridional element ismicrofabricated.
 11. Intraocular pressure recording system according toany of the previous claims 1 to 9 wherein at least one of saidcontinuous longitudinal or meridional element is a wire.
 12. Intraocularpressure recording system according to any of the previous claims 1 to11 wherein said contact lens (1) furthermore comprises other measuringdevices such as an ElectroRetinoGraph or a chemical analysis sensor. 13.Intraocular pressure recording system according to any of the previousclaims 1 to 12 wherein it comprises several active gages (2). 14.Intraocular pressure recording system according to any of the previousclaims 1 to 13 wherein it comprises several passive gages (5). 15.Intraocular pressure recording system according to any of the previousclaims 1 to 14 wherein it comprise four gages in a Wheatstone bridgeconfiguration, such as two active gages and two passives ones beingplaced alternatively on the bridge.